Polycaproamide having excess number of carboxyl end groups over amino end groups



C. POLY CAPRO AMIDE HAVING EXCESS NUMBE June 4, 1968 TWILLEY ,3

E OF CARBOXYL END GROUPS OVER AMINO END GROUPS Tram; .350: uw mm E5552 v n. x 2 9 b Om wN 0N VN NN ON Filed Jan.

LYN 3 1 ad I Qm ALISODSM 113W B3ON3QV8Q .40 90 1 INVENTOR IAN C.TWILLEY ATTORNEY United States Pate 3,386,967 POLYCAPROAMIDE HAVHNG EXCESS NUMBER OF CARBOXYL END GROUPS OVER AMlNO END GROUPS Ian C. Twilley, Petershurg, Va., assignor to Allied Chemical Corporation, New York, N.Y., a corporation of New York Continuation-impart of application Ser. No. 368,028, May 18, 1964. This application Jan. 19, 1965, Ser. No. 426,632

6 Claims. (Cl. 260-78) This application is a continuation-in-part of my US. application S.N. 368,028 filed May 18, 1964.

This invention relates to improved fiber-forming polycaproamide and to continuous multifilament polycaproamide yarn of improved strength andtoughness, obtainable from said polycaproamide.

Yarns of polycaproamide, otherwise known as nylon 6, find widespread use in applications which can benefit from the high strength, suppleness, uniformity and durability of said yarns. Typical applications include high strength webbing such as safety belts, protective coverings such as tarpaulins, netting, and reinforced structures such as tires, conveyor belts and power transmission belts. In these industrial applications of synthetic yarns, improvements in strength and toughness are continually sought since such improvements increase the effectiveness of the yarn in a particular utilization, or permit the use of less yarn to obtain satisfactory performance. The specific properties of the yarn which are of primary interest in the aforesaid textile structures are the ultimate tensile strength, which is the force required to break the yarn, and the toughness index or the total mount of work required to break the yarn.

It is generally known that the tenacity of polycaproamide yarn can be increased by drawing the yarn to a higher state of molecular orientation. This expedient, however, results in a decrease in the ultimate elongation of the yarn, tending to diminish the toughness index. Moreover, highly oriented cords exhibit increased shrinkage at elevated temperatures which, in turn, may create difliculties during subsequent fabrication of reinforced rubber structures. Another general approach toward improving the tenacity of polycaproamide yarn is to employ higher molecular Weight polymer in the production of said yarn. However, as the molecular weight of the polycaproamide is increased, there is generally an attendant increase in the viscosity of the molten form of the polymer, and this makes more diflicult the production of yarn by standard melt extrusion methods. To reduce its viscosity, thus facilitating extrusion through the small orifices of the spinnerette, the polymer can be brought to higher spinning temperatures than the usual range of 250 to 290 C., but degradation of the polymer then sets in causing production of weak, discolored, non-uniform yarn.

It is an object of this invention to provide a polycaproamide of comparatively low melt viscosity relative to its number average molecular weight. It is another object of this invention to provide a continuous multifilament yarn of improved strength from polycaproamide having a number average molecular weight previously considered too high to permit satisfactory melt spinning. Other objects and advantages will appear hereinafter.

The above and other objects and advantages are achieved by this invention which comprises a linear, fiber-forming e-polycaprolactam wherein the end groups are susbtantially all primary amino groups and carboxyl groups, the primary amino groups being not over about 20 milliequivalents per kilogram of polymer (hereinafter expressed as meq./kg.). The total content of end groups Patented June 4, 1%68 "ice of my polycaproamide analyzes not over about 135 .meq /kg. This polycaproamide is characterized by a relatively low rate of increase of melt viscosity as the number average molecular weight of the polymer increases, i.e. as the total content of end groups goes down. The melt viscosity of the polymer can be determined in apparatus wherein shear is applied to the melt, one particular such apparatus being the Brabender plastograph. Measured as'described below with this plastograph, the logarithm of melt viscosity of my polycaproamide, plotted against number average molecular weight of the polymer, increases at a rate not above 6X l0 units per molecular weight unit.

My preferred polymers have number average molecular weights Well above those ordinarily suitable for spinning of polycaproamide, whereby particular advantage is realized from the relatively low melt viscosity of my polymers at high number average molecular weights. These preferred poly-caproamides have been about 50 and about 80 meq./kg. of total end groups, corresponding to number average molecular weights from about 25,000 to about 40,000; have primary amino group analysis not above about 10 meq./kg.; and show Brabender melt viscosity at 265 C. not above about 500 units.

My polymers can be produced by polymerizing e-caprolactam and reacting the polymer with a dibasic carboxylic acid containing at least 6 carbon atoms per molecule. In the reaction with the dibasic carboxylic acid, the primary amino end groups of the polycaproamide react with the carboxyl groups of the acid. One carboxyl group of the acid may react, thereby eliminating one primary amino group from the polymer and providing a second carboxyl end group in the polymer, this being the second carboxyl group of the dibasic acid. In the alternative, both carboxyl groups of the dibasic acid can react with primary amino groups of the polymer thereby eliminating two primary amino groups. Whichever of these reactions occurs, in the final polymer the content of combined dicarboxylic acid will be about equivalent to one half the excess of carboxyl groups analyzed in the polymer over primary amino groups analyzed therein. Suitable quantities of dicarboxylic acid or similarly reactive derivative thereof for use in producing our polymers are about 0.l0.7 mol per 100 mols of lactam, the acid having between 6 and suitably about carbon atoms. T o produce the preferred high molecular weight polymers of our invention, the proportion of dicarboxylic acid preferably used is about 0.2-0.4 mol per 100 mols of lactam.

As will be appreciated, my invention includes the above polymers in the form of continuous filaments e.g. a multifilament yarn, drawn to impart permanent elongation and showing, by X-ray analysis, molecular orientation along the filament axis. The preferred polymers can be formed into such filaments having very high ultimate tensile strength (U.T.S.) of 9.5 grams per denier and higher, combined with very high toughness index of at least 40 as measured by the product of U.T.S. and square root of ultimate elongation at the break.

The accompanying drawing is a graph showing relation of Log 10 of Brabender melt viscosity to number average molecular weight for three polycaproamides, viz:

(A) Contains -40 rneq./kg. of primary amino groups (i.e. milliequivalent of primary amino groups per kilogram of polymer) representing prior art;

(B) Contains 10-15 meq./-kg. of primary amino groups;

(C) Contains the preferred range of less than 10 meg/kg. of primary amino groups.

In a preferred mode of carrying out my invention the polycaproamide composition of the present invention is prepared by polymerization of e-caprolactarn in the presence of a dibasic carboxylic acid and water, at elevated temperatures. The polymerization can be carried out batchwise or continuously.

Ordinary polycaproamide has roughly equal proportions of amine and carboxyl end groups. When it has been produced using a dibasic acid in the reaction mixture as chain terminator or viscosity stabilizer, for example, as in the normal termination of the known polycaproamide with adipic acid as a viscosity stabilizer, the resulting polycaproamide analyzes about 35-40 meq./kg. of primary amino end groups and about 65-60 meq./kg. of carboxyl end groups and has number average molecular weight of about 20,000.

The polymers of the present invention contain not more than 20 milliequivalents of amino end groups per kilogram of polymer (abbreviated hereinafter meq./kg.) and have number average molecular weight of at least about 15,000. To attain the desired low level of primary amino groups in the polymer especially when the polymer has the preferred high number average molecular weight of 25,000 and above, we have found it is necessary to force the reaction of amino and carboxyl groups beyond the level reached in the usual polymerization processes. In particular we have found the special polymerization method described in U.S. Patent 3,109,835 of Apostle et al., of Nov. 5, 1963 suitable for producing our preferred polymers of high molecular Weight and low primary amino group content.

The dibasic carboxylic acid employed in the present invention can be aliphatic, alicyclic, aromatic, or alkylaromatic, and must contain at least 6 carbon atoms. Representative suitable species include aliphatic acids such as adipic, pimelic, suberic, azelaic, sebacic, undecanedioic, dodecanedioic and tetradecanedioic; aromatic dicarboxylic acids such as terephthalic acid, alieyclic species such as cyclohexane 1,4-dicarboxylic acid; and heterochain species such as the his carboxymethyl ether of ethylene glycol. The dicarboxylic acid can contain substituent groups which are non-reactive with amine or carboxyl groups in the course of the polymerization reaction. In general, the dibasic acid must be thermally stable and non-volatile under the conditions of polymerization, and will suitably contain 6-20 carbon atoms per molecule. In stead of the acids themselves, carboxy derivatives thereof, reactive with primary amino groups, can be used to form the polycaproamides of this invention, e.g. dibasic acid monoand diesters, dibasic acid anhydrides, etc.

By way of contrast, mono-functional carboxylic acids, regardless of their chain length are found ineffective in providing high molecular weight polymers of low melt viscosity. Trifunctional carboxylic acids have been found to give non-linear chains, resulting in less desirable fiber properties. Aliphatic dicarboxylic acids having fewer than 6 carbon atoms have been found ineffective in producing the polycaproamide composition of this invention perhaps because of their instability and tendency to cyclize during the polymerization process.

A suitable process for producing these polycaproamides involves including in a molten polymerization reaction mixture about 0.1-0.7 mole of dicarboxylic acid per 100 moles of lactam monomer. At the usual polymerization temperatures of about 240-290 C., and in the presence of these amounts of dicarboxylic acid in the polymerization reaction mixture, equilibrium is approached between the carboxyl groups and primary amino groups in the polymerization reaction mixture at number average molecular weight not above about 20,000 under usual atmospheric pressure polymerization conditions; and at least about 30 meq. of primary amino groups per kilogram of polyamide remain present by analysis. Accordingly special measures are required to carry the reaction of the carboxyl groups and amino groups further. A particularly useful method of accomplishing the required further reaction is to remove volatile by-products of the polymerization such as water by flowing at least 2 unit volumes (S.T.P.) of inert gas, capable of removing moisture from the reaction mixture, across the reaction mixture surface per hour per each unit volume of the reaction mixture. Other means which can be used include application of vacuum for prolonged periods during polymerization; and solid state polymerization methods carried out for long periods upon the polymer. Preferred products are obtained under the above conditions and using about 0.2-0.4 mole of dibasic acid per 100 moles of lactam.

The number average molecular weight of a given polymer is determined from the relationship:

Where NH =milliequivalents of amino end groups per kilogram of polymer, and COOH=milliequivalents of carboxyl end groups per kilogram of polymer. Carboxyl groups are analyzed by dissolving a polymer sample in benzyl alcohol and titrating with sodium hydroxide solution in benzyl alcohol, to the phenolphthalein end point. Primary amino groups are analyzed by dissolving a polymer sample in m-cresol and titrating with p-toluenesul fonic acid solution in methanol, to the thymol blue end point.

When acetic acid is used as chain terminator, the milliequivalents of acetyl end groups per kilogram of polymer is determined and is added to the other two end group determinations to give the denominator for determining number average molecular weight:

The acetyl groups are analyzed by dissolving a polymer sample in a 3:1 by volume mixture of phosphoric acid/ o-xylene; distilling off the o-xylene/ acetic acid azeotrope; and titrating it with aqueous sodium hydroxide to the phenolphthalein end point.

It will be recognized that the minimum number average molecular weight of polymer in accordance with this invention (viz, about 15,000) corresponds to total content of end groups of about 135 meq. per kg. of polymer; and the preferred minimum number average molecular weight of 25,000 corresponds to about meq. of end groups per kg. of polymer. In terms of F.A.R.V. i.e. the standard formic acid relative viscosities per ASTM D-789-62T, number average molecular Weight of 15,000 is about 30-35 F.A.R.V.; 20,000 is about 60-70 F.A.R.V.; and 25,000 is about -100 F.A.R.V. for ordinary polycaproamides; and for polymers of this invention these molecular weights correspond to about 25-30, 40-50 and 55-65 F.A.R.V. and 30,000 number average molecular weight is about 90-95 F.A.R.V.

Prior to spinning, a polymer of this invention may be made to contain various property-modifying additive ingredients such as: flame retardant agents selected from compounds of antimony, phosphorus, and halogen; titanium dioxide delustrant; antistatic agents, adhesion promoting agents including isocyanates, epoxides, and their derivatives; heat and light stabilizers such as inorganic reducing ions; metal ions such as manganese, copper and tin; phosphites; and organic amines such as alkylated aromatic amines and ketone-aromatic amine condensates; thermally stable pigments such as Quindo Magenta (Allied Chemical Corp.) and inorganic pigments; fluorescent agents and brighteners such as Tinopal PCR; latent cross-linking agents; bacteriostats such as phenols and quaternary amines; colloidal reinforcing particles; antisoiling agents; compatible and incompatible fiber-forming polymers such as linear fiber-forming polyesters; and other known additives.

The additives can be incorporated into the polymer generally at any stage of polymerization, as concentrates distributed in monomer or in preformed polyamide, or as pure ingredients. When added as pure ingredients, care must be taken during addition to facilitate the rapid dispersal of the additive throughout the polymer system. This is especially true when the additive is of a corrosive nature and, in pure form would react with metal apparatus. In such cases, corrosion can be minimized by introducing the additives to the caprolactam feed stream via a tube of non-corrosive material which exhausts into the center of said stream and cocurrent therewith. It is also generally important when incorporating these additives, as is known, to obtain a good dispersion thereof in the polymer in order to obtain high quality filaments upon spinning.

It will be appreciated that the polycaproamide of this invention can contain minor amounts of units other than caprolactam in the polymer chain, e.g. p-carboxybenzylamino units and the like.

Melt viscosity measurements for the purpose of the present invention were made using a Brabender plastograph Model PLV-3 (C. W. Brabender Instruments, Inc., South Hackensack, NJ.) equipped with a stainless steel roller type mixing head Model G88 which masticates the polymer. The mixing head has an 88 cc. mixing chamber capacity containing two intermeshing rollers mounted on a rotatable shaft. The torque generated is measured on a dynamometer. In the test method, a 35 gram sample of polymer to be tested is added to the mixing chamber over a 2 minute period, said sample having been dried at 120 C. for at least 2 hours prior to testing. The mixing chamber is supplied with dry nitrogen which blankets the test specimen, and the chamber is maintained at 265 C. The viscosity at 60 rpm. roller mixing speed is recorded on a chart within 5 to minutes after the polymer is melted. Sensitivity of the device is set at its highest level where 1,000 Brabender units equal 1,000 meter-grams.

Because the geometry of the Brabender mixing chamber is complex, measurement in the conventional units of the rheologist, i.e. shear-stress (dynes-centimeter shear rate (per sec.), and poises is not possible. It is thus more convenient to correlate the melt viscosity characteristics of different polymers in terms of the viscosity reading of the Brabender unit. Ordinary polycaproamide having a number average molecular weight of 21,000- 23,000, considered the upper limit for normal commercial melt spinnability, will have a Brabender test value of 350-500 Brabender units. a

As illustrated in the accompanying drawing, the log of the Brabender melt viscosity of linear polycaproamides of given amino end group content approximates a straight line function of the number average molecular weight of these polyamides. Thus as shown by line B of the drawing, the melt viscosity of polymer of the present invention containing about 10-15 milliequivalents of amino end groups per kilogram of polymer approximately obeys the following equation:

log of Brabender melt viscosity 1.046+(.05S7 10 Mn) wherein Mn equals the number average molecular weight.

With polymers of the present invention containing not above 8 milliequivalents of amino end groups per kilogram of polymer, the following equation represented by line C of the drawing is found applicable in relating the number average molecular weight to the melt viscosity:

log of Brabender melt viscosity =1.025+(.0487 10 x Mn) For comparison, the melt viscosity of normal polycaproamide of the prior art having 30-40 meq./kg. amino end groups is found to be given approximately by the equation:

log of Brabender melt viscosity =1.017+(.0736 l0 Mn) which is represented by line A of the drawing.

By way of example, for a number average molecular weight of 26,000, a polymer of the present invention containing about 12 milliequivalents of primary amino groups per kilogram of polymer will have a Brabender melt viscosity of about 300. A polymer of this invention containing fewer than 8 milliequivalents of amino end groups per kilogram of polymer, will have a Brabender melt viscosity of only about 150 or so. A polycaproamide of the prior art of the same number average molecular weight viz. about 26,000 and having equal proportions of amino and carboxyl end groups will have 38 milliequivalents of primary amino groups per kilogram of polymer and will have a Brabender melt viscosity of over 800. It is thus apparent that, at the number average molecular weight of 26,000 exemplified above, the polymer of the present invention will have a melt viscosity 60%80% lower than ordinary polycaproamide of the prior art. Such lowered melt viscosity allows melt spinning polymers of higher molecular weights than can normally be spun to produce the higher strength yarns of this invention.

The melt spinning of the polyamide of this invention can be carried out using any technique generally suitable for melt spinning polycaproamides. For example molten polymer, at a temperature of 250 C. to 290 C., the higher temperatures being employed with the higher molecular weight compositions, is pumped through filter means such as a bed of sand or screens or both, and thence through the orifices of a spinnerette plate. Upon emerging from the orifices, the extruded filaments pass downward through a quenching zone wherein the molten polymer extrudate is solidified to form continous filaments. Conventional cooling gas can be employed such as air, nitrogen, carbon dioxide, steam, etc., at controlled temperature and fiow rate. The gas will generally be fiowed'co-current, counter-current, or cross-current to the filaments in one or more distinct regions, and can be quiescent in the zone around the spinnerette.

A preferred spinning technique, which allows spinning at higher melt viscosities than usual, is to employ quiescent heated inert gas around the spinnerette, with temperatures in the quiescent zone at least 40 C. higher than the temperature of the polymer melt as it reaches the spinnerette, as disclosed and claimed in the copending US. Application of Swanson, Harlacher and Dulin, Serial No. 426,631 filed January 19, 1965.

The drawing of the as-spun yarn to produce molecular orientation along the filament axis can be accomplished by conventional operations. Suitably the yarn passes via a feed roll to a drawing zone wherein the yarn is subjected to tension and an elevated temperature in the range of -200 C., from which the yarn is withdrawn by a draw roll having a faster peripheral speed than the feed roll. The draw point can be localized by means of a snubbing pin which may be heated or unheated, rotatable or nonrotata'ble. Controlled yarn temperatures may be secured by various means such as: heated contact surfaces which may be flat or curved; radiant heating means; heated baths; heated vapors suitably confined to a region surrounding the travelling yarn; and other suitable means. The ratio of a certain length of yarn after drawing to the length of the same mass of material immediately prior to drawing, or the ratio of the peripheral speeds of the draw roll to feed roll, provided there is no yarn slippage thereon, is the draw ratio of a drawing operation, and is normally expressed for example, as 4 or 5 where the ratio is respectively 4 or 5. The yarn of the present invention is preferably drawn using a non-rotating draw pin, and auxiliary heating means to secure a draw ratio in the range of 4.0 to 6.5. The yarn may be drawn in a single or multiple stages.

Tenacity measurements of the yarn of this invention were carried out with a Scott Tensilgraph IP4 using Spruance air-operated cord clamps and a gage length of 10 inches. A total weight of 10 kilograms was used including the carriage weight of 2 kilograms. At least four breaks on each sample are taken so that 4 breaks will fall within one half inch on the load scale; these are then averaged to ascertain the tensile strength. The ultimate elongation is likewise so determined on a Scott Tensilgraph by observation of the extended length of the yarn sample at its breaking point.

The toughness index is essentially the area under the stress-strain curve of a yarn sample from the origin or zero stress point out to the breaking point, and thus represents essentially the total amount of work required to rupture the fiber. For high strength polycaproamide yarn, the area under the stress-strain curve, and thus the toughness index, may be approximated by the formula -UTS(UE) wherein UTS is the ultimate tensile strength in grams per denier and UE is the ultimate elongation in percent as determined on an IP4 Scott Tester. The practice of this invention is further illustrated in the following examples, wherein all parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 400 pounds of epsilon caprolactam and 0.45 percent by weight, i.e. 1.8 lbs. of sebacic acid (0.25 mole per 100 moles lactarn) were charged to a kettle equipped with a heating jacket and a horseshoe agitator. A trace amount of copper compound soluble in the reaction mixture, and a small amount of ketone/diarylamine condensation product as in Schule U.S.P. 3,003,995 of October 10, 1961, were incorporated in the reaction mixture as heat stabilizer.

Polymerization was accomplished generally as in the above cited Apostle et al., U.S. Patent 3,109,835 of Nov. 5, 1963, except for the initiation which involved first applying steam pressure of 50 p.s.i.g. to the space above the fluid in the vessel, heating to 255 C. within 1 hour, and holding the temperature of the mixture at 255 C. for 1 hour under the 50 p.s.i.g. steam pressure. The steam pressure was then gradually released and the vessel returned to atmospheric pressure, maintaining the temperature of the polymerization mixture at 255 C. The surface of the smoothly stirred reaction mixture was then swept with dry nitrogen gas at a rate of about 10 liters per minute i.e. about 34 unit volumes of gas measured at standard temperature and pressure (S.T.P.) per hour per unit volume of the reaction mixture, for approximately 10 hours. At this time, which represented 12.8 hours at the 255 C. temperature, further increase in viscosity was very slow.

The polymer was extruded into a warm water bath and chopped into pellets by ,5 inch in size. The pellets were then hot water washed at 100 C. to reduce the content of hot water soluble constituents to about 12% by weight; and the pellets were dried to less than 0.1% moisture. The polycaproamide thus produced was found to have a number average molecular weight of 30,800. It is designated A in Table I below.

For purposes of comparison, polycaproamide polymer C of like number average molecular weight to polymer A was prepared by the process of this example, but omitting the sebacic acid. The polymer melt was so viscous as to require special high strength motors to effect adequate agitation for temperature control in the polymerization kettle.

In order to provide for comparative testing of polycaproamide made with monocarboxylic acid additive, polymer B having about the same melt viscosity shown by the above polymer A was prepared by the procedure of this example, except using acetic acid (instead of sebacic acid) at a concentration of 0.28 mole percent in the polymerization reaction mixture. The properties of the several polymers prepared are presented in Table I.

The polymers prepared hereinabove were melt spun at polymer melt temperature of 262 C. into a quenching tower employing air as the cooling medium. The air flowed co-current with the filaments for the major course of their travel through the quenching tower. In the region just below the spinnerette, the air was maintained quiescent and was heated to a temperature of about 335 C. by an annular shield around the spinnerette in accordance with copending U.S. application of Swanson, Harlacher and Dulin No. 426,631 filed Ian. 19, 1965. Such use of heated quiescent gas was found to give optimum yarn properties; however, such is not essential and the same procedure except that the tower has no heated annular shield can also be used effectively, as shown in Table I below. The quenching tower had a gas exhauster to remove caprolactam vapor evolved from the filaments as they passed through the quiescent air zone, generally as described and claimed in the copending U.S. application of Dulin Ser. No. 262,546 filed Mar. 4, 1963, now U.S. Patent 3,257,487. The take-up speed of the filaments TABLE '1 Polymer Characteristics Additive Sebucic Acetic None Acid Acid Number average molecular weight 30, 800 20, 400 31,100 Brabeuder melt viscosity 350 335 2, Carboxyl end groups 58 49 31 Amino end groups 7 22 32 Yarn Characteristics With W ithollt With Unspiuheated heated heated nable shield shield shield Draw ratio 4. 9 4. 9 4. 7 Denier 840 840 841 Ultimate tensile strength (g.p.d.), i.e., UTS 10. 1 J. 85 9. 35 Ultimate elongation percent,

i.e., UE 18.1 17.8 16.5 Toughness index,

UIS(UE)% 43.0 41. (i 38.0

lvlilliequivalents per kilogram of polymer (carboxyl end groups do not include the acetyl end groups of polymer B, which amount to 27 meq. per kg. of polymer).

exiting from the quenching tower was about 1,800 feet per minute. The yarns were subsequently drawn by passage first over a snubbing pin and then over a heated plate maintained at C. The propertie of the yarns thus prepared are presented in Table I.

As the data of Table I show, yarn prepared from the high molecular Weight spinnable polymer of the present invention, has considerably higher ultimate tensile strength and considerably higher toughness index than yarn spun by the same procedure from a polymer obtained using a conventional acid terminated polymer, having about the same melt viscosity, but having lower molecular weight.

The polymer having essentially the same molecular weight as that of the above polymer of the invention, but made without chain terminator, had much too high melt viscosity to be spinnable to yarn.

EXAMPLE 2 A series of polycaproamide polymers was prepared using the polymerization procedure of Example 1, cmploying O.20.4 mole percent sebacic acid, and utilizing progressively shorter reaction times and/ or applying water vapor pressure to secure polymers of progressively lower molecular weights having generally increasing contents of primary amino groups in the range about 10-15 meq. per kilogram of polymer. A series of comparison polymers was prepared similarly but omitting the sebacic acid and using approximately 60% lower inert gas sweep rate whereby comparable molecular weights were achieved in about the same reaction times.

The molecular weights and Brabender melt viscosities of the polymers are recorded in Table II. By plotting the Log of the melt viscosity vs. the molecular weight of the polymers with 10-15 meq./kg. of primary amino lo'g of melt viscosity: 1.0464+ (.0557 X X Mn) tion mixtuire gives a lowered melt viscosity at a number average molecular weight of 2l,000-22,000 as compared to no additive, even though the extent of reaction of amine end groups with the acid, reached at this molecular AS u be 11 mm 9116 of Table Ordinary P 3!- 5 weight level, left unreacted primary amino groups amountcaproami-de of molecular weight 21,900 has too high a TABLE III melt viscosity to permit satisfactory melt spinning. The

O1 y Moles of Number Brabcnder p yinei of the present invention, as exemplified in this Mdmves caprolactam Average Belt example, contain n .21 mole percent sebacic acid, has a Bar Mole 6r Molecular Viscosity melt viscosity which permits melt spinning up to a molec- 10 Dlabasw Acld Welgilt ular weight of about 28,000. The use of preferred amounts Piinelie Acid 380 26, 600 285 Suberie Acid. 380 26, 750 292 ofdica rboxylie acid, as exemplified elsewhere herein, per Ammo Am 415 27, 600 340 mits the spinning of polymers of even higher molecular ie pa ie X10 415 27,800 340 1 ipie 01 415 27,400 360 weight, ranging as high as 37,000. g fi g 415 267700 637 r' uccinie or 415 25,700 050 EXAMPLE 3 gnleeanegioic 201g 324 25,000 249 A series of dicanboxylic acids were evaluated to deter- Tfidiiiliidlli lg/ id 2.1% 23:28?) 510 mine their suitability for producing the low melt viscosity, gggg qi ffi xg g2 28% 213 high mfJlecuIar weight polycaproamides of this invention. g P t fi x g" 324 241800 249 I 1 1 oniop 1 1a ie ei 380 26, 580 283 The po ymerization procedure of Example 1 was employed 2, 7 Nap Malena Dicarboxync using a polymerization tempfirature of 255 1C. for a Acid 280 26,490 291 period of 12 to 14 hours. T e additives e-mp oyed and the results obtained are presented in Table III. mg to meg/kg Polymer' The mUghHQSS Index a A L I the tensile strength of the yarns are seen to increase with T B E I increasing molecular weight of the polymer. The Bra- N b A Brabender Melt Viscosity bender melt viscosity is seen to be dependent upon the um er verage Molecular Weight Polycaprpamide Ordinary Polycaproamide molecular -g and the a ino eI ld group analysis.

er i ntain i with -40l1 '1el./kg. of The polymers of the present invention, represented by e pnmary ammo gmups products D, E, F, G and H, made with at least .2 mole 14,500 72 120 percent sebacic acid, have primary amino group analysis 17,000... 80 186 30 170 320 below 20 milliequivalents of amine per kilogram of poly- 21,900-.- 193 405 mer. The preferred products have number average molec- 24 700 245 722 1 340 1,198 ular weights of at least 25,000 and primary amino group 23.38% 32% figg analysis not above about 10 meq./kg., represented by r products D, E and F of Table IV. Continuous multi- (11015 tmilgie(41uivz1ilents of gmigw e -cup p kilogram of p filament yarns of this invention, melt spun from products 2 7 mi lliequivalents of amino end groups per kilogram of polymer. D, E: and l y the provedure of 'p 1 have Made with .25 mole percent sebacic acid. a toughness index greater than 40 and a tensile strength As the data of Table III indicate, the dicarboxylic acids of at l ast 9.5 grams per 0611161. employed having at least carbon atoms and up to about 40 EXAMPLE 5 20 carbon atoms are eifective in producing high molecular weight, low melt viscosity polymer. A dicanboxylic acid of A of slmllar pfl y p Was stuflled fewer than 6 Cambon atoms, namely .glutaric acid, was determine the effect of increased molecular weight on found substantially ineffective since, at the number aveir- Y P p Whllfi malmalmng melt VISCOSIW age molecular Weight f the polymer O-btained, the melt r constant at about 350 Brabender units. The several viscosity was essentially the same as ordinary polycapro- P y pl were P p y the P F 9 amide made without any i b li acid Example 1 using about 0.2-0.3 moles of sebacic acid A P 4 per 100 moles of caprolactam and varying inert gas flow M LE rates and reaction times whereby at higher flow rates A study was made of the inter-relationship of melt and/or higher times, the higher molecular weights and viscosity, molecular weight, and amino end group content lower amine analyses were obtained, shown in Table V. if polycaproamides made with varying proportions of Higher amounts of sebacic acid give a lower content of sebacic acid. These polycapiroamides were prepared by the primary amino groups in the polymer for given molecular TABLE IV Mole Total Hours Sweep Gas 'lough- End Group Analysis Number Brabender Ultimate Sample Percent of Iolyinerizer Rate, Liters ness Average Mcl t 'lensrle Sebacie on Per Minute Index Amine Carboxyl Molecular Viscosity Strength Acid Temperature Weight 99 9. 0 6 37. 0 50 51 19,800 340 9. 33 .08 9. 5 6 37. 2 35 67 19, 000 342 9. 4 14 s. 5 6 37. 5 27 70 21, 500 945 9. 45 24 13. 5 10 40. 9 10 62 26, 900 350 9. s 24 16. 0 10 41. 9 9 63 27, 209 348 10.0 .24 1s. 5 10 43. 2 7 58 .500 352 10. 17 .35 16. 0 19 37.8 s 83 22, 500 193 9. 43 61 16. 0 10 34. 0 s 122 15, 400 so 8. 5

l Milliequivalents per kilogram of polymer. procedure of Example 1, except that the flow of sweep weight of the polymer. These polymers were spun essengas, and the duration of polymerization were varied as tially as in Example 1. The viscosity of the polymer melt shown in Table IV, to obtain products all having about the being spun was adjusted to the exact value of 350 same high but still spinnable melt viscosity (about 340- Brabender units by setting the temperature of the melt 350 Brabender units at 265 C.) when possible; or to 70 to the required level determined by test in the Brabender app-roach maximum obtainable melt viscosity, when the proportion of sebacic acid used was above about 0.3 mole per 100 moles of lactam (e. g. 0.35 mole percent in the table). The data of Table IV show that use of as little apparatus.

The spinning temperatures used, and the nature of the polymers and yarns prepared, are presented in Table V. As the data of Table V indicate, in yarn spun from as 0.15 mole percent of sebacic acid in the polymerizapolymer at the same melt viscosity, yarn properties such 11 as ultimate tensile strength and toughness index are significantly improved by use of polymer of higher molecular weight, said phenomenon being observed at molecular weights as high as 34,200 in this example. Moreover at a given molecular weight level these properties are somewhat higher in the polymer which, by virtue of its lower primary amino group content, was spun at the lower temperature.

EXAMPLE 6 This example illustrates production of high strength polyeaproamide yarn from a dispersion of synthetic linear polyester in a polycaproamide of this invention.

Granular polyethylene terephthalate polymer was used, melting about 255 C. (DTA) and about 265 C. (optical), having density (when amorphous) of about 1.33 gm. per ml. at 23 C., and about 1.38 gm./ml. in the forms of drawn filament, having reduced viscosity of about 0.85 and having 'IT about 65 C. The polyester in the form of drawn filament drawn to give ultimate TABLE V Spinning Temper- Number Grams per Toughness ature C.) Average Moleeu- Denier Index r Weight Tenacity Terminal Amines 11-14 1 Terminal Amines 8-10 Terminal Amines Less Than 7 1 Milliequivalents of primary amino groups per kilogram of polymer.

elongation not above 20% will have tensile modulus (modulus of elasticity) ranging from about 70 to about 140 gm. per denier, depending on spinning conditions employed.

This polyester analyzed about 58 milliequivalents of carboxyl groups and about 60 meq. of hydroxyl groups per kilogram. Carboxyl groups in the polyester were determined by dissolving the sample in benzyl alcohol at about reflux temperature of the alcohol and immediately cooling the solution at room temperature for a few seconds, and pouring into chloroform. The resulting solution was titrated with sodium hydroxide in benzyl alcohol to the phenolphthalein end point. The polyester hydroxyl groups were determined by heating a solution of polyester in l-methylnaphthalene with succinic anhydride for 4 hours at 175 C. and purifying the resulting polymer by precipitating in ethanol, redissolving in l-methylnaphthalene, reprecipitating in ethanol, filtering, and drying; then analyzing for carboxyl groups as above outlined. The increase in millimols of carboxyl groups over the original value is taken as the value for the hydroxyl.

groups in the sample.

This polyester (30 parts) was mixed with 70 parts of granular polycaproamide having reduced viscosity (measured at 25 C. and 0.5 gm./ 100 ml. concentration, in purified o-chlorophenol containing 0.1% water) of about 1.04 dl./gm., T about 35 C. and density about 1.14 gm. per ml. at 23 C. Amine groups in this polycaproamide had been blocked by reaction with sebacic acid, bringing the amine group analysis thereof to 11 milliequivalents of NH groups per kilogram of polymer, as determined by dissolving a sample of the polymer in o-cresol and titrating with p-t0luenesulfonic acid in methanol to the thymol blue end point. This polycaproamide contained as heat stabilizer, 50 p.p.m. copper as cupric acetate.

The mixture of polyamide and polyester granules was blended in a double cone blender for 1 hour. The granular blend was dried to a moisture content of no more than 0.01%; then melted at 285 C. in a 3 /2" diameter screw extruder operated at a rotational speed of about 39 rpm. to produce a pressure of 3000 p.s.i.g. at the outlet. A dry nitrogen atmosphere was used to protect the blend against absorbing moisture. Residence time in the extruder was 8 minutes.

The molten mixture thereby obtained had melt viscosity of about 2000 poises at 285 C. The polyester was uniformly distributed throughout and had average particle diameter of about 2 microns, as observed by cooling and solidifying a sample of the melt, leaching out the polyamide component with formic acid, and examining the residual polyester material.

The molten mixture was pumped through a filter pack including a series of screens and a sand bed under a pressure of 2000 p.s.i.g. and at a temperature of 285 C., and was extruded through a spinneret plate having 136 orifices of circular cross section, each of said orifices having a diameter of .013 inch. The resulting filaments proceeded downwardly through a quenching chamber containing air at 82 C. and relative humidity fiowing cocurrent to the filaments at a rate of about 37 cubic feet per minute. The yarn was taken up onto a cylindrical package below the quenching chamber at a speed of 1350 feet per minute under a tension of 40 grams. Just prior to packaging, a lubricating finish was applied to the yarn to the extent of about 5% pick-up based upon the weight of the yarn. The yarn thus obtained has an approximate denier of 4600 and a birefringence of .006.

The yarn thus produced was then subjected to a drawtwisting operation by running the yarn to an upper draw roll provided with a cot roll to prevent yarn slippage, then in a single Wrap about a stationary ceramic drawpin of 1%" diameter, then to a contact surface heater at C., and then in five wraps about a lower draw roll and associated separator roll. By operating the lower draw roll at a peripheral speed 5.4 times faster than the upper draw roll, the yarn was drawn 5.4 times its initial length. The yarn was subsequently wound onto a pirn at a rate of 840 feet per minute using a ring-traveler device so as to impart 0.4 turns per inch of twist to the yarn. The yarn thus obtained is found to have the properties which in Table A below are compared to the properties of a polycaproamide yarn produced similarly but without incorporating polyester therein.

Formic acid leaching of the drawn yarn and micro scopic examination showed presence of dispersed polyester microfibers having an average diameter of about 0.20.4 micron and average length of 40-60 microns. These fibers lay generally lengthwise of each filament and numbered at least 2,000 through a 1,000 square micron filament cross section.

The fatigue resistance was measured upon a yarn like that of this example but containing 40 ppm. of copper and 0.3% by Weight of BXA (trade name of a Naugatuck Chemical Div. antioxidant further described in US. Patent 3,003,995 to Schule, issued Oct. 10, 1961); and

13 was compared to that of a standard nylon 6 tire yarn of known very excellent fatigue resistance, using the Goodrich disc fatigue test (ASTM-D-885). The yarn of this invention thus tested showed at least 90% of the fatigue resistance of the standard nylon 6 tire yarn used for comparison.

I claim:

1. A linear fiber-forming e-polycaproamide wherein the end groups are substantially all primary amino groups and carboxyl groups; wherein the total end groups analyze between about 50 and about 80 milliequivalents per kilogram of polycaproamide; the primary amino groups analyze not above about milliequivalents per kilogram of polycaproamide; and the melt viscosity in Brabender units at 265 C. is not above about 500.

2. Polycaproamide of claim 1 containing sebacic acid combined therein in an amount about equivalent to onehalf the excess of carboxyl groups in the polymer over the primary amino groups-therein.

3. Polycaproamide of claim 1 in the form of a continuous filament showing, by X-ray analysis, molecular orientation along the filament axis.

4. Filament of claim 3 formed of polycaproamide having total end group content in the range of 50-80 milliequivalents per kilogram of polycaproamide and primary amino end group content not above about 10 milliequivalents per kilogram of polycaproamide, the polycaproamide forming said filament having sebacic acid combined therein in amount about equivalent to one half the excess of carboxyl groups in the polycaproamide over primary amino groups therein; said filament having ultimate tensile strength of at least 9.5 grams per denier and having toughness index of at least 40.

5. Process for the production of a high molecular weight, low melt viscosity polycaproamide comprising forming a molten polymerization reaction mixture at about 240-290 C. from, as essential. ingredients, e-caprolactam and about 0.1-0.7 mol, per 100 mols of lactam, of a dicarboxylic acid having between 6 and 20 carbon atoms per molecule; and smoothly stirring said reaction mixture while flowing over the surface thereof a gas capable of removing moisture from said reaction mixture, at flow rate of at least 2 unit volumes of said gas, measured at standard temperature and pressure, per hour per each unit volume of said reaction mixture, until the totalprimary amine group plus carboxyl groupanalysis of the resulting hot water washed and dried polymer is not above about 135 meq./kg. and the primary amino group analysis thereof is not above about 20 meq./kg. these analyses being in units of milliequivalents per kilogram of polymer. 7

6. Process of claim 5 wherein the polymerization is initiated by water; the proportions of dibasic acid used in forming the reaction mixture are about 0.20.4 mol per 100 mols of 'caprolactam used in forming the reaction mixture; and the analysis of total primary amino groups plus carboxyl groups in the washed and dried polymer is not above about meq./kg. and the analysis of primary amino groups therein is not above about 10 meq./ kg.

References Cited UNITED STATES PATENTS 2,989,798 6/1961 Bannerman 260- 78 3,109,835 11/1963 Apostle et al. 260-78 2,241,322 5/1941 Hanford 26078 2,241,323 5/1941 Greenwalt 260-78 2,551,702 5/ 1951 Prochazka 26078 2,805,214 9/1957 Zimmerman 260-78 3,003,222 10/1961 Pitzl 260-78 3,047,541 7/1962 Pyifel et al 26078 3,090,997 5/1963 Au 26078 3,093,881 6/ 1963 Zimmerman 260-78 FOREIGN PATENTS 766,120 6/1954 Germany.

935,696 11/ 1955 Germany.

890,437 2/ 1962 Great Britain.

WILLIAM H. SHORT, Primary Examiner.

S. H. BLECH, Examiner.

H. D. ANDERSON, Assistant Examiner. 

1. A LINEAR FIBER-FORMING E-POLYCAPROAMIDE WHEREIN THE END GROUPS ARE SUBSTANTIALLY ALL PRIMARY AMINO GROUPS AND CARBOXYL GROUPS; WHEREIN THE TOTAL END GROUPS ANALYZE BETWEEN ABOUT 50 AND ABOUT 80 MILIEQUIVALENTS PER KILOGRAM OF POLYCAPROAMIDE; THE PRIMARY AMINO GROUPS ANALYZE NOT ABOVE ABOUT 10 MILLIEQUIVALENTS PER KILOGRAM OF POLYCAPROAMIDE; AND THE MELT VISCOSITY IN BRABENDER UNITS AT 265*C. IS NOT ABOVE ABOUT
 500. 